In the printing field it is common to form a shingled stream of paper sheets, for example, after a large sheet of paper is printed in, for example, an offset printing machine. This large sheet can be folded and cut to provide so-called cut sheets which can be advanced in a shingled pattern, i.e. with each sheet overlapping and overlapped by adjacent sheets in the advance of the stream.
The cut sheets may be provided in such manner that two folded cut sheets are derived from each large sheet and two cut sheets can then be oriented so that an upper sheet with its fold opposite the lower cut sheet can be coextensive with it, i.e. can completely cover the lower sheet of the pair so that the borders of the two cut sheets of the pair coincide exactly.
Just as individual cut sheets can be shingled, it is possible that a main stream of cut sheets in a shingled pattern may have pairs of such cut sheets disposed in the shingled array so that each pair, in turn, overlaps and is in turn overlapped by adjacent pairs of sheets.
Where the pairs of cut sheets are shingled and an upper shingle overlies a lower shingle of the pair, it is desirable to separate the upper sheets from the lower sheets. In the past this picking or culling of the upper sheets from the lower sheets to establish, for example, two partial streams of shingled sheets has been done by hand at relatively high personnel cost.
In Swiss patent 655,489, it is taught to separate or split a sheet stream of shingled sheets but this requires that the upper and lower sheets of each pair of shingles be offset from one another so that they can be engaged by different forms. The technique of this patent is not suitable where the shingles or cut sheets are provided in pairs and, within each pair, are coextensive with one another.
Swiss patent 663,604 describes a deflecting device for a sheet stream of, for example, brochures, signatures or sheets (shingles). A plurality of conveyor paths are provided and connect to one another. A partial stretch form, a branch and is swingable so that the travel direction can be changed for the various items advanced in the main stream. This can allow a diversion of the stream of paper articles through 180.degree..
In general, therefore, a system which permits splitting of a main stream of shingled sheets in which the shingled sheets are provided in coextensive pairs has not been available for automatic and low-cost separation of the sheets of the pair and the formation of two shingled partial streams of the sheets as is frequently desirable.